Cathode ray tube



June 1, 1943- w. FLECHSIG CATHODE RAY TUBE Filed Oct. 16, 1940 2Sheets-Sheet l Fly. 2

INVENTOR W FLEC/I'S/G "w 770 NEV June 1, 1943. w. FLECHSlG CATHODE RAYTUBE 2 Sheets-Sheet 2 Filed Oct. 16, I940 INVENTOR W FL ECHS/G BY TJUZNEV Patented June 1, 1943 CATHO'DE RAY TUBE Vierner Flechsig,

Berlin- Charlottenburg,

Ger-

many; vested in the Alien Property Custodian Application October 16,1940, Serial No. 361,379 In Germany November 8; 1939 13 Claims.

The invention reiates to cathode ray tubes and in particular to tubesfor television purposes.

It is an object of the present invention to improve cathode ray tubes inwhich the cathode ray is deflected over a screen in one or twodirections. It is a further object to overcome the difficulties whicharise when the cathode ray has a different angle of incidence on variousparts of the screen surface. It has been suggested to curve the screenin such a manner that the center of curvature thereof coincides with thecenter of deflection of the deflecting systems so that the cathode rayhas a vertical direction to the screen at all points of the screensurface. Such a curvature of th screen is, however, undesirable in manycases. If, for example, an optical image is produced on a photoelectricmosaic screen, it is preferable to employ an optical system of normaldesign producing a sharp image in a plane. In such a case the mosaicscreen cannot be curved but must be plane because otherwise the opticalimage would not be sharp.

According to the invention, an electron-optical lens system is arrangedbehind the deflecting field in the direction of the cathode ray so thatit is situated between the deflecting field and the screen of the tube.The focal point of this lens system coincides at least approximativelywith the center of deflection of the deflecting system.

The effect of this lens system may be easily eX- plained by comparisonwith a light optical sys term. If a source of light is arranged at thefocal point of a collecting lens, the divergent bundle of rays emittedby the source of light is made parallel. the deflected electron bundleincluding a larger or smaller angle with the axis of the system inaccordance with the degree of deflection is made parallel to the axis ofthe system by the lens. The deflection itself remains practicallyundisturbed. In. the same manner the electronoptical image is onlyslightly influenced thereby. The additional lens produces an additionalslight collection of the rays resulting in a small shortening of thtotal focal length.

If the invention is carried out in connection with a tube having twodeflecting systems for two diflerent directions, it is preferable to usedeflecting systems having coinciding centers of deflection. A mixedmagnetic and electric or a purely magnetic deflecting system may beutilized at which both deflecting devices are arranged in the samedistance from the cathode or the screen. Another possibility consists inusing deflecting systems at diflerent distances from the cathode In asimilar manner the central ray of and employing two additionalcylindrical lens systems arranged vertically to each other,the focalpoints of said cylindrical lenses coinciding with the centers ofdeflection of the respective deflecting systems.

Other aspects of my invention will be apparent or will be specificallypointed out in th descrip tion forming a part of this specification, butI do not limit myself to the embodiment of the invention hereindescribed, as various forms may be adopted within the scope of theclaims.

Referring to the drawings,

Figs. 1 and 2' show the optical equivalents of two electron-opticalsystems according to the invention;

Fig. 3 shows a cathode ray tube in longitudinal section corresponding toFig. 1; and

Fig. 4. shows a cathode ray scanning tube in longitudinal section,employing a system according to Fig. 2.

A cathode ray bundle 2 is emitted by a cathode i. It is concentrated byan electron-optical lens 3 so that under the influence of this lensalone a sharp spot is produced at point 4. The space 5 represents theeffective area of two deflecting fields arranged vertically to eachother and having a common center of deflection 6. The deflected cathoderay i represented by lines I2 and has a concentrating point 1. Thecentral ray includes an acute angle with the screen. By means of theadditional lens 8, however, the focal point of which coincides with thecenter of deflection (i of the deflecting system, th bundle is deflectedso that its central ray is directed parallel to the axis of thearrangement as indicated by dotted lines. As the additional lens 8 hassimultaneously a certain but limited concentrating power, the focalpoint i produced in a plane 9 situated closer to the lens 8 than thepoints 4 and l. The plane 9 is the image plane for all angles ofdeflection. This arrangement has the advantage that the cathode raybundle has a vertical angle of incidence over the entire screen surface.

The additional lens 8 may have the form of a concentrating coil. It maybe in the form of a so-called long coil surrounding the entire spacebetween the lens plane and the image plane 9. Such a coil has the effectof guiding theelectrons in paths substantially parallel to the axis ofthe coil. The stray field at the left side of the coil is used fordeflecting the rays into the parallel direction.

If an electrostatic lens is used it may be an accelerating or adecelerating lens. In both cases the lens may have the form ofcylindrical elements or wall coatings which are separated by a suitablespace. A decelerating lens should be chosen if the velocity of impact ofthe electrons on the screen is to be small.

Fig. 3 shows an embodiment for such a case. The tube envelope 2|contains a cathode I. The cathode rays are accelerated by an anode l9and further accelerated by a wall coating 24. A concentrating coil 22 isthe equivalent of lens 3 of Fig. 1. The deflecting system consists oftwo pairs of deflecting coils 23. The screen 26 is a mosaic screenconsisting of photoelectric elements. An optical image is produced bylens 21 and projected upon the mosaic screen. A wall coating 25 ofcylindrical form together with the wall coating 24 forms the additionaldecelerating lens 8. The coating 24 has a potential of +100 volts andthe coating 25 a potential of volts against the cathode so that theelectrons arrive at the screen with a velocity of only +10 volts andcannot liberate secondary electrons. The arrangement is made in such amanner that the field of the electrode having the higher potential of100 volts does not extend to the screen. A certain minimal distanceshould therefore be provided. An accelerating lens may be used if theelectrons are to arrive at a fluorescent screen with high velocity andproduce a strong light effect.

The arrangement of Fig. 2 contains a ray producing and deflecting systemof similar form. The cathode ray tube itself with the cathode I,concentrating coil 22 and deflecting system 23 is represented in Fig. 4.In this arrangement the cathode ray bundle is additionally deflected byan electron-optical prism, the effective area of which is represented inFig. 2 by the circle I0.

This field is, for example, produced by two coils 23 situated on bothsides of the tube. The coils are fed by direct current so that ahomogeneous magnetic field is produced having a direction vertical tothe plane of Fig. 4. The light optical system II is arranged on the sameside of the screen as the electron optical system. The lens 8, formed bythe cylindrical electrodes 24 and 25 is arranged between theelectron-optical prism I0 and the screen 9 so that the cathode rays havea right angle of incidence upon the screen. The tube may be used asimage scanning tube for television transmission. In this case the screen26 is a photoelectric mosaic screen. In another embodiment the tube isprovided with a fluorescent screen 26. The light produced by the screenis then projected by lens I l upon a projection screen which is notrepresented in the drawings.

tire field to be scanned in paths normal to the plane of said surfacedespite the action of said deflecting means.

2. The combination of elements as in claim 1 in which said targetcomprises a surface which emits light when impacted by electrons.

3. In combination, means for generating a' beam of electrons ofrelatively small cross-sectional area, a target member which presents asubstantially planar surface to said beam, means for deflecting the beamover a two-dimensional field on said surface to scan said field, thedeflecting systems for the two perpendicular directions of deflectionhaving coinciding centers of deflection, and means including anelectron-optical lens between said deflecting means and said target tocause the beam to approach said target substantially normal to the planeof said surface despite the action of said deflecting systems.

4. The arrangement according to claim 3 in which each of the twodeflecting systems is of the magnetic type.

5. The arrangement according to claim 3 in which the focal point of saidelectron-optical lens concides with said centers of deflection of saiddeflecting systems.

6. In combination, means for generating a beam of electrons ofrelatively small cross-sectional area, a target member which presents asubstantially planar surface to said beam, means for deflecting the beamover a two-dimensional field on said surface to scan said field, andmeans including an electron-optical lens between said deflecting meansand said target to cause the beam to approach the target throughout saidentire field to be scanned in paths normal to the plane of said surfacedespite the action of said deflecting means, said electron-optical lenscomprising two cylindrical surfaces surrounding different portions ofthe axis of the undeflected beam, said surfaces being placed atdifferent potentials.

7. In combination, means for generating a beam of electrons ofrelatively small cross-sectional area, a target member which presents asubstantially planar surface to said beam, means for deflecting the beamover a two-dimensional field on said surface to scan said field, andmeans including an electron-optical lens between said deflecting meansand said target to cause the beam to approach the target substantiallynormal to the plane of said surface throughout said entire field to bescanned, said electron-optical lens comprising a plurality ofelectrostatic lens elements, the lens element nearest the target beingplaced at a relatively low potential so that the electron strike thetarget at a relatively low velocity.

8. In combination, means for generating a beam of electrons ofrelatively small cross-sectional area, a target member which presents asubstantially planar mosaic surface to said beam, said mosaic surfacebeing adapted to have radiations applied thereto from an object or fieldof View, means for deflecting the beam over a two-dimensional field onsaid surface to scan said field, and means including an electron-opticallens between said deflecting means and said target to cause the beam toapproach the target throughout said entire field to be scanned in pathsnormal to the plane of said surface despite the action of saiddeflecting means.

9. In combination, means for generating a stream of electrons, a targetfor at least a portion of the electrons in said stream, means comprisinga pair of deflecting systems for deflecting said stream over atwo-dimensional field on said target in two directions at right anglesto each other to scan said field, and means including anelectron-optical lens system between the deflecting systems and thetarget tocause the electrons of the stream to approach the targetthroughout said entire field to be scanned in paths normal to thesurface of the target despite the action of said deflecting systems, thefocal point of said lens system at least substan tially coinciding withthe center of deflection of the deflecting systems.

10. In combination, an electron discharge de vice having an enclosurecomprising a first portion having means for generating a beam ofelectrons therein, and a second portion attached to said first portionand having a target structure for said beam therein, the axis of thesecond portion making an acute angle with the axis of the first portion,means for bending said beam so that the axis thereof in the undefiectedposition substantially coincides with a normal to the surface of saidtarget taken through the center of the portion thereof to be contactedby the beam, means for deflecting the electrons in said beam while theyare in the first portion of said enclosure to cause the beam to scan atwo-dimensional field on said target, and electron-optical means locatedaround the path of the beam between said deflecting means and saidtarget to cause the beam to approach the target throughout said entirefield to be scanned in paths normal to the plane of said surface despitethe action of said deflecting means.

11. The combination of elements as in claim 10 in which said bendingmean comprises a magnetic electron-optical prism.

12. The combination of elements as in claim 10 in which saidlast-mentioned means comprises two spaced spherical electron lenselements l0- cated within the second portion of the enclosure, theselens elements being placed at dilferent potentials.

13. In combination, means for generating a beam of electrons ofrelatively small cross-sec tional area, a target member which presents asusbtantially planar mosaic surface to said beam, said mosaic surfacebeing adapted to have radiations applied thereto from an object or fieldof view, means for deflecting the beam over a two-dimensional field onsaid surface to scan said field, and means including an electron-opticallens system between said deflecting means and said target to cause thebeam to approach the target throughout said entire field to be scannedin paths normal to the plane of said surface despite the action of saiddeflecting means, said lens system comprising two spaced lens elements,these elements being placed at different potentials, the focal point ofsaid lens system coinciding at least approximately with the center ofdeflection of said deflecting means.

WERNER FLECHSIG.

